1. Field of the invention
The present invention relates to a semiconductor light-emitting device and, more particularly, to a semiconductor light-emitting device with high light-emitting efficiency and better color rendering property.
2. Description of the prior art
The so-called “white-light” usually refers to a mixed light of multiple light sources with different colors. The white-light that is visible for human beings includes at least two colored lights with at least two wavelengths. For example, mixing blue-light and yellow-light can get a two-wavelength white light. Mixing blue-light, green-light, and red-light can get a three-wavelength white light.
Nowadays, no matter it is a household illuminating apparatus, such as a fluorescent lamp, a U-shaped electricity-consuming bulb, a small flashlight, or an illuminating apparatus inside cars, air crafts or ships, light emitted from such illuminating apparatus belongs to a three-wavelength white light. In addition, the back-light source of the TFT-LCD also belongs to a three-wavelength white light. This proves that white light-emitting modules have taken a considerably large proportion in the market of illuminating apparatus.
White light-emitting diodes (WLED) in the prior art mainly include two types. The first type includes multiple LED chips, and white light is generated by adjusting the current passing through each single-colored LED chip. Besides, the first type can also be divided into a three-wavelength WLED using a red-light LED chip, a blue-light LED chip and a green-light LED chip; and another two-wavelength WLED using a yellow-light LED chip and a blue-light LED chip. Although the first type of WLED has higher light-emitting efficiency, fabrication cost is higher due to the use of multiple single-colored LED chips.
The second type uses a blue-light LED chip combined with a yellow inorganic fluorescent powder (or a yellow organic fluorescent dye) to emit white light. The blue light emitted from a blue-light LED chip has a wavelength between 440 nm and 490 nm. After being illuminated by the blue light, the yellow inorganic fluorescent powder can emit yellow-colored fluorescence which is mixed with the blue light to generate the white light. Compared to the first type of WLED, the second type of WLED is easier to be fabricated and is cheaper, thus present commercially available WLEDs mostly belong to the second type of WLED.
However, because the second type of WLED has lower light-emitting efficiency and is a two-wavelength WLED (mixture of a blue light and a yellow light only), its performances on the color rendering property and the color temperature are worse than those of a three-wavelength WLED. Therefore, the existing drawbacks of the second type of WLED need to be improved.
Therefore, the main scope of the invention is to provide a semiconductor light-emitting device with high light-emitting efficiency and better color rendering property.